The proposed project is intended to identify and isolate retrovirus from dogs and characterize its morphological and biochemical features. Endogenous and exogenous retroviruses have been isolated from various animals and human beings. However, until now no conclusive evidence for the existence of a canine retrovirus has been put forth. Animal models are being used extensively not only to study pathologic mechanisms of the human immunodeficiency virus (HIV) and human T-lymphotropic virus (HTLV) but also to identify and screen antiretroviral drugs and vaccines. Although, currently there is no conclusive evidence for animal retroviruses inducing a clinical disease in human beings caution is always suggested in dealing with infected animals. Dogs are the most preferred companion animals for humans. In the present study, we plan to use both the traditional methods and the more recent biotechnological methods to search for the canine retroviruses and then characterize them. We propose to use transmission electron microscopy, isolation of the virus from replication permissive cell cultures, demonstration of reverse transcriptase activity in culture supernatants, and reverse transcriptase polymerase chain reaction (RT-PCR) technique to demonstrate virions in the culture supernatants. The identify of the virus will be determined by sequencing of the amplified products following molecular cloning. In order to further characterize the virus, we will study the cross reactivity of the isolated canine retrovirus with other known retroviruses using immunoblotting technique determine its buoyant density in sucrose gradients and study the preference of its reverse transcriptase to Mg++ or Mn++. Apart from its veterinary importance, identification and isolation of a canine retrovirus may provide a model for not only further delineating the molecular mechanisms in the pathology induced by human retrovirus but also to plan antiretroviral strategies. Further, isolation of a retrovirus from dogs may provide an important link in our understanding of interspecies retrovirus relatedness and perhaps of their pathogenesis.